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PREFACE 
The study of the mechanical and physical conditions in the deep interior 
of the stars is undertaken primarily in the hope that an understanding 
of the internal mechanism will throw light on the external phenomena 
accessible to observation. More than fifty years have gone by since the 
general mode of attack was first developed; and the scope of the inquiry 
has grown so that it now involves much of the recently won knowledge of 
atoms and radiation, and makes evident the ties which unite pure physics 
with astrophysics. It would be hard to say whether the star or the electron 
is the hero of our epic. 
The reader will judge for himself whether solid progress has been made. 
He may, like Shakespeare, take a view less optimistic than my own— 
The heaven’s glorious sun 
That will not be deep-searched with saucy looks ; 
but I hope he will not be so unkind as to continue the quotation— 
Small have continual plodders ever won 
Save base authority from others’ books. 
Re-reading this work I find passages where I have been betrayed into too 
confident assertion. It is only too true that the most patent clues may 
mislead, and observational tests of the rough kind here possible sometimes 
flatter to deceive. But the subject is a fair field for the struggle to gain 
knowledge by scientific reasoning; and, win or lose, we find the joy of 
contest. 
The last two chapters trespass beyond the ground indicated by the 
title of the book. This extension can perhaps be justified; but I am aware 
that, whatever excuse I might make, the real reason was that I could not 
forgo a desire to collect and review some of the remarkable researches of 
those who have investigated the outer layers of a star. 
The book was written between May 1924 and November 1925. Time 
was occupied by a number of minor investigations made to fill the gaps 
that disclosed themselves as the material was brought together. Anyone 
writing on a theme which many workers are actively investigating is liable 
to find his pen unable to overtake the rate of growth of the subject. During 
the above-mentioned period the theoretical papers on stellar constitution 
in the Monthly Notices alone amounted to more than 400 pages. It has 
been still more difficult to cope with modifications and progress in the 
theory of the atom, on which astronomical developments must rest. As 
we go to press a “new quantum theory” is arising which may have 
important reactions on the stellar problem when it is more fully developed.